The invention relates to a plant for cleaning the exhaust gases from a cement rotary kiln, which comprises at least one reduction catalyst with a honeycomb-shaped basic pattern for gaseous pollutant components and a dust separator.
Industrial furnace plants which are used in the cement industry always constitute a specific problem with regard to gas cleaning. As well as the high exhaust gas temperature of for example 250-400.degree. C., the dust structure influenced by the construction of the heat exchanger and the cyclic processes performed is problematical. Exhaust gases are produced which contain dust and gaseous components. The solid components have been precipitated with increasing efficiency for decades. In relation to the gaseous constituents, the exhaust gas cleaning has only recently achieved a state which can be regarded as environmentally tolerable. During combustion, in addition to CO and hydrocarbons, in particular nitrous oxide compounds known as NO.sub.x are produced which must also be removed. Under particular peripheral conditions, in particular in strong sunlight and with a high concentration of hydrocarbon compounds in the environment, within hours an ozone excess attributable to a nitrous oxide content can be generated which exceeds the tolerance limits. The nitrous oxides also contribute to the formation of acid in the atmosphere because part of the NO.sub.2 is transferred into nitrous acids.
One technically perfected process available is catalytic denitrification, in particular with a selective reduction catalyst (SCR). Here in the state of the art for example ammonia is injected into the exhaust gas flow which causes the nitrous oxide contained in the exhaust gas to be converted into nitrogen and water on the catalyst surface.
EP, A1 0519225 describes an industrial furnace plant with a first filter stage for removal of dust from the exhaust gases to be cleaned. In at least one further filter stage, the exhaust gases cleared of dust are cleaned of the NH.sub.x compounds and/or volatile pollutant elements and compounds contained by at least partial NO.sub.x reduction with the use of a carbon-containing filter medium. The filter dust precipitated in the first filter stage is processed and passed for recycling.
DE, A1 3601917 describes a process for cleaning exhaust gas, in particular the exhaust gases from waste combustion plants, of nitrous and sulphur oxides, hydrocarbons, dioxins and dust. The exhaust gases from the combustion plant are passed via a secondary burning chamber with a primary and secondary dust filter to a DENOX catalyst, a first reduction catalyst, in which the nitrous oxides and where applicable sulphur oxides are reduced to elementary nitrogen or sulphur. In a chain of further assemblies, the cleaned exhaust gas is passed to a stack.
Dust separators structured as electric filters are described for example in the journal Zement-Kalk-Gips (ZKG International) Vol 35 (1982) Ed. 10, pages 509 to 518. The emphasis is placed on dust removal, in particular conditioning of the dust particles with water before introduction to an electric filter. Instead of an electric filter, for dust removal also filtering precipitators, for example hose filters, can be used. The exhaust gas cleaned of dust can then be passed to at least one reduction catalyst for removal of the gaseous pollutants.
The present invention is based on the task of creating a plant to clean the exhaust gases of a cement rotary kiln of the type described initially which can be used in particular in the cement industry with a high degree of efficiency of the catalyst, which works practically maintenance-free and which eliminates the pollutants in one working process without the production of residual substances. Special and further design forms of the invention are the object of the dependent patent claims.